Answer:
The main reason so few African leaders are replaced in free elections is because the vast majority of African nations have serious socio-political and economic problems, which generate enormous political instability and serious situations of social tension. Thus, for example, countries like Mali have 75% of their population living on less than 2 dollars a day, while others, like Nigeria, increase this percentage to 92%.
Thus, these situations of poverty, need for primary resources and lack of opportunities generate social conflicts that, translated into politics, are the starting point for revolutions, dictatorships and other anti-democratic manifestations.